The aim of this work is to understand how a cell coordinates the expression of its genetic repertoire during normal growth and during nutritional deficiency. One component of this process is a regulatory nucleotide, guanosine 3',5'-bispyrophosphate (ppGpp) whose discovery and characterization have been described in previous reports. This report is concerned with cellular regulation of ppGpp concentrations and regulatory effects of ppGpp. On the basis of mutant studies it appears that the concentration of ppGpp is thought to participate in the coordination of expression of about half the E. coli genes during nutritional imbalance but has virtually no noticeable regulatory effects during normal growth. Lethal consequences of the relS mutation abolishing ppGpp accumulation during energy source starvation are described here. Work continues towards determining the structural basis of gene promoter activity by engineering ribosomal RNA gene alterations. Two assays of these alterations are being developed involving gene fusions and sensitization of in vitro systems by genetic modification to eliminate nuclease activities.